Electrical device



Feb, 19, 1946. w. c, sLAUsoN ELECTRICAL DEVICE i Filed May 28, 1942 ATORA/Ev TTES ELECTREGTL DEVEE Application May 2s, wie., sci-iai No. (ci. 20cice 7 Claims.

This invention relates to electrical devices and particularly to the construction of electrical contact assemblies wherein a plurality of contact members are arranged in a stack and are sepa rated by insulating members.

In electrical devices of the above character, such as electromagnetic relays, jacks, keys, and the like, it is the usual practice 'to' arrange the spring Contact members in a stack or pile-up in which the contact members are interposed between insulatedy strips and in which outer compression plates having bolts extending through aligned apertures of the pile-up clamp the entire group into a compact assembly. It is also customary to insulate the bolts from the spring members by enclosing each bolt with an insulated bushing. In devices manufactured in accordance with the above practice the contact springs thereof often become shortv circuited with one another by the presence of loose metallic particles such as metal chips or Silvers, which, during the manufacturing process, fall into the inter stices between the outer surface of the insulated bushing and the circumferential edges of the spring members. Engagement of the chips with adjacent spring members produces a short circuit which can be corrected if detected during inspection, but due to the migration of the chips, in a relay. for example, during shipment and also after installation in a telephone exchange, shorts appear that were not apparent during the testing or inspection period with consequent loss in circuit and maintenance time. Several remedial expedients have been proposed heretofore such as the use of pliable rubber bushings, of length slightly longer than the over-ail pile-up, which when compressed expand laterally to prevent longitudinal movement of the chips. Although the above pliable rubber bushing arrangement reduces the number of short circuits in spring pile-ups the reduction thereof is insuilicient because of the lach of complete radial expansion along the entire length of the bushing so that more effective and yet at the same time economical means are highly desirable.

It is therefore an object' of this invention to overcome the above disadvantages and to provide an improved and simplied construction for a Contact spring pile-up.

Another object of the invention is to interlock the insulated bushing with the elements of -a contact spring pileeup.

A further object of the invention is Ito construct a contact spring pile-up in which migration of slivers and chips is prevented in interstices yspace between the outer surface ci the bushing' I 'use of an overlcng cellulose acetate bus assembling the various elements thereof into loose pile-up, dipping the assemblyinto a sollic tion of a cellulose acetate solvent, such as acetone, and then compressing the assembly whereby softened acetate bushing iiows radially into the and circumferential. edges of the openings in th members uhrough which the 'bashing estende, forming cornparatiteiv rigid extrnsicns thereon upon evaporation ne solvent.

Another feature ci the invention resides in the ing contact spring piie-np in which the assembly is 'first compressed and the solvent later applied with the resultant softening and extrusion or 'the bushing, as described almveo These and other features of the invention will be more fully described in the following specification, taken in connection with ythe accompanying drawing in which:

Fig. l illustrates a telephone relay having a contact spring plie-np at the right end thereof;

Fig. 2 illustrates a ercssmsecticnal view of the spring pile=up shown in Ii'ig. l in which the overlong cellulose acetate bushing 'nd other elements thereof are depicted in a loosely assembled ccndition;

Fig. 3 illustrates a cross-sectional View ci the compressed pilewup taltenalcng of Fig. It;

Fig. 4 illustrates another embodiment ci the invention in which a slot is provided in the upper clamping plate the application of the solvent; and

Fig. 5 illustrates a crosssectional view taken along line Sue ci Fig. fr showing the slot in greater detail. n

Referring now to the drawing and particularly to Fig. 1, there is shown a telephone relay it oi a well known type, which comprises the usual winding il, armature i2, contact springs i3 arranged in a pile-up or stack assembly ifi, and e frame i8 for supporting said members. The spring pile-up comprises alternate contact springs I3 and insulation strips il superposed upon one another, a spring member l li for dexlbl; supporting armature i2... clamping plate l, and bolts or screws 2| for securing pile-up Il to frame I6 and also for compressing the members of pile-up Il into acompact unit. Contact springs I3 are provided with terminal portions 22 for connection to external wiring. Inasmuch as the principles of construction and operation of relaysare well understood, a more detailed description thereof is unnecessary, especially since they do not form a part of the present invention.

Referring partlcuiarly to Figs. 2 and 3, sectional views of spring pile-up I4 illustrate in greater detail the assembly of' the various elements constitutng the pile-Sup. In Fig. 2.is shown a loose assembly of the component parts, particularly bushing or sleeve 23 which is slightly longer than the over-alliength of the pile-up, the excessive length being indicated approximately by the space between the inner edges of clamping plate I9 and uppermost insulation strip Il. A bushing having an overlength of approximately it; inch has been foundto be suitable. Bushing 23 consists of an insulated comparatively rigid material, such as cellulose acetate, that is capable of being temporarily softened by a volatile solvent, such as acetone, and after being so treated assumes the modified form. Screw 2l is surrounded by bushing 23, the combination thereof extending through aligned openings 2l formed in springs I3, I8 and insulation strips I'I, while screw 2l threadedly engages frame I and extends by itself through opening 25 in clamping plate I8. It is to be noted that spaces or interstices- 26 appear between the outer surface of bushing 23 and the circumferential edges of the contact springs I3 and insulation strips l formed by the openings 2l. It is also to be noted that the upper and lower edges of bushing 23 abut the inner surfaces of clamp ing plate I9 and frame IB respectively.

In the manufacture of contact springs I3 burrs (not shown) often adhere to the circumferential edges oi' the openings 24 thereof and upon assembly of the springs into a stack these burrs chip ofi.' and reside in the interstices 26 so that when several chips (not shown) or a chip of sufficient length becomes lodged between adjacent contact springs I3 of a pile-up a short circuit results thereacross. Upon inspection of the assembly this short circuit is readily discovered but if the chips at the time of inspection do not contact adjacent contact springs I3 the relay is passed as being satisfactory. Later, because of movement of the relay, that is, as a result of shipment from the manufacturing plant and installation in the telephone exchange, the chips tend to migrate within the interstices so that conmt may occur between adjacent springs I2, after the relays have been cut into service. From a manufacturing standpoint it is not economically practical to eliminate the burrs and chips entirely so that the next best expedient is to freeze whatever chips that are present in the assembly into place, thereby preventing subsequent migration of the chips. This is accomplished effectively by eliminating the interstices 2B, in other words, by filling up these spaces 26 through the radial expansion of bushing 23.

In one embodiment of the invention, the loosely assembled contact spring pile-up, shown in Fig. 2, is first dipped into a volatile solvent (not shown) lsuch. as acetone, in order to temporarily soften the cellulose acetate bushing 23, then withdrawn from the solvent, after which the pile-up I4 is compressed to its ultimate size, as shown in Fig. 3, either by screws 2l or by al suitable compressing mechanism, as for example the fixture disclosed in Patent 2,129,869 issued September 13, 1938 to Harold S. Pike, screws 2I serving to retain the applied pressure to the pile-up upon removal of the compressing mechanism. By this softening the overlong cellulose acetate bushing 23 and then shortening it to size by longitudinal compression bushing 23 is forced to expand or flow radially thereby filling up the interstices 2B formerly present between the outer surface of bushing 23 and circumferential edges of apertures 24 in springs I3 and insulation strips II. Any chips present thereinare therefore effectively sealed or frozen in place by the extrusions formed on bushing 23 in an economical and practical manner. Upon evaporation of the solvent, which is volatile, the bushing 23 with the extrusions formed thereon rehardens and assumes the set of the interstices.

In another embodiment of the invention, the spring pile-up Il is first compressed and the solvent then applied to the overlong bushing 23. In order to satisfactorily apply the solvent to bushing 23 access must be provided therefor. A means for accomplishing this is illustrated in Fig. 4 where the clamping plate I8 is provided with a slot 2l, shown more clearly in Fig. 5, extending from an edge of clamping plate I9 to aperture 25 thereof. As in the above first-mentioned embodiment the members of the spring` pile-up are first assembled into a loose stack Il; however, in this embodiment, the next step consists in compressing the members thereof in a manner already described so that overlong bushing 23 is under pressure between clamping plate I9 and frame I B. The solvent (not shown) is then applied by a hypodermic syringe (not shown), or some other equivalent means, through slot 21 to bushing 23, which as it becomes softened expands radially because of the pressure to fill the interstices 26 formerly between the outer and inner circumferences of bushing 23 and apertures 2l, re spectively, of the contact springs I3 and insulation strips I1. Upon evaporation of the solvent, as mentioned hereinbefore, bushing 23 returns to its original state of rigidity with permanent extrusions formed thereon. Any chips or slivers that may have been lodged within the interstlces 26 are therefore effectively sealed in place. To facilitate access of the solvent to bushing 23 more than one slot may be provided and these slots may be placed either in the top or bottom of pile-up Il or may be placed in both clamping plate I9 and frame I6.

While this invention has been shown and described as embodying certain features merely for the purpose of illustration, it is, of course, understood that various modifications may be made in the details thereof and that the features may be applied to many other and widely varied fields without departing from the scope of the invention yas defined in the appended claims. For example, the cellulose acetate bushing 23 may be softened by heat, as by a spot welding machine, in the above-mentioned second embodiment.

What is claimed is:

1. The process of making an electrical stack which consists in superposing alternate layers of apertured insulating strips and contact elements upon an apertured base, inserting an overlong insulating bushing into said strips and elements. placing an apertured clamping plate over said v bushing, securing said base, strips, elements, and

plate into a. unit assembly by a bolt, subjecting the assembly to a volatile plasticizer for temporarily softening the bushing and, applying pressure to the assembly whereby the bushing is expanded laterally to interlock with the strips and elements.

2. The process of making an electrical contact assembly consisting in superposing in alternate layers, insulator strips and contact elements having apertures therein, placing the strips and elements upon a frame provided with similar apertures, a'igning said strips, elements, and frame so that said apertures provide a continuous opening through the assembly, inserting an overlong cellulose acetate bushing into said opening. placing a clamping plate having an aperature/over said bushing with the aperture in alignment with the opening, securing said strips, elements, frame and plates together -by a bolt, subjecting the assembly to a volatile plasticizer for temporarily softening the bushing, and applying substantial pressure upon the plate and frame whereby said bushing because of its overlength is caused to expand laterally to interlock the bushing with said strips and elements.

3. The process of making an electrical spring pile-up which consists in superposing in alternate layers, insulated strips and contact springs having perforations therein, mounting said strips and springs upon a frame having similar perforations, aligning said perforations to produce continuous openings through the pile-up, inserting overlong cellulose acetate bushings into said openings, placing a plate having perforations over said bushings with the perforations in alignment with the openings, arranging said pile-up into a loose assembly by bolts threadedly engaging the frame, dipping the loose assembly into a through the pile-up, inserting tubular overlong cellulose acetate bushings into said openings,

placing a clamping plate having perforations over said bushings with the perforations in line with theopenings, inserting into said openings bolts, applying substantial pressure to the plate and frame whereby the bushing is contracted. and

vinJecting a volatile liquid solvent into the area of the bushing whereby extrusions are formed on the bushings, said extrusions occupying the space between the bushing and edges of the strips and contact springs and sealing any chips in place.

5. 'I'he process of making an electrical stack which consists in constructingan assembly of alternate layers of insulated strips and contact springs secured by a bolt enclosed with a comparatively rigid overlong insulated bushing, temporarily softening said bushing, applying pressure to the 'assembly so that the softened bushing is expanded laterally to interlock with the strips and elements, and permitting the bushing to reharden. l

6. An electrical spring pile-upkk comprising alternately disposed conducting springs and insulating strips, said springs and strips having axially aligned holes of different diameters forming a bore having a plurality o f internally projecting ledges, a bushing disposed in said bore and having a plurality of-integrally formed protrusions which illl the spaces between the ledges internally projecting from the bore, and means for clamping said springs, strips and bushing together to form a unitary structure.

7. In a stacked electrical spring assembly, a

plurality of superimposed conducting springsv having holes of substantially equal diameters, in-

sulating strips therebetween having holes of diameters dierent from the diameters of -the holes of said conducting springs whereby, when said springs and insulating strips are arranged in stacked formation with the axes of the holes thereof in alignment the stack is characterized by a bore having a plurality of irregularities, an

insulating bushing disposed in said bore and hav- 

